Fix issues found on x-series charts

[jotak]

Follow-up on #98

• Fixed bar charts overlaping on left axis
• Won't display overlay when xAxis type is series (timeless)

[jotak]

@lucasponce this fixes the comments you had.
Now bars are more centered to prevent them overlapping over left axis:

[lucasponce]

On my screen I get these ones:

• x-series with bars looks ok:
  

-x-series with scatters looks weird when it touches the x-axis, but nothing to change IMO:

But I see a couple of minor issues that also found in Kiali and are a little bit annoying:

• Empty logo should be centered:
  

• Same happens on error cases:
  

On wide screens it's more visible, perhaps in a standard view it looks horizontally centered, but I guess on empty/errors, that element could be centered with the available width.

In Kiali with the two columns of charts, it's more visible and empty logos look strange, I think.

[jotak]

Thanks. I'll merge it, the issue on error/empty is really unrelated, i'll investigate apart.